Synergistic Electron-Proton Transfer Over In₂O₃/CuGa_0.5S Z-Scheme Heterojunction for Highly Selective CO₂-to-CH₄...

Solar-driven photoconversion of CO₂ and H₂O into value-added chemicals such as CH₄ remains a promising yet challenging strategy, hindered by inefficient charge separation and sluggish proton migration kinetics. Herein, an interfacial-engineered Z-scheme In₂O₃/CuGa_0.5S heterojunction is designed to synchronize electron transfer with proton delivery. Utilizing Kelvin probe force microscopy, a direct Z-scheme charge-transfer pathway with electron accumulation on CuGa_0.5S is identified. Electronic-state modulation facilitating CO₂ activation is revealed by quasi-in situ XANES and operando XPS, while water dissociation is promoted by In-O sites on In₂O₃ for continuous reactive H* supply. Preferential H* relocation to CuGa_0.5S and coupling with *COOH intermediates are demonstrated by in situ DRIFTS and DFT calculations, through which continuous hydrogenation toward CH₄ is driven. Key intermediates are stabilized by synergistic interactions between adjacent components, resulting in significantly enhanced CH₄ selectivity and effectively suppressed competing H₂ evolution. Consequently, a CH₄ evolution rate of 319.2 µmol g^-1 h^-1 with approximately 100% selectivity is achieved over optimized In₂O₃/0.5CuGa_0.5S in pure water. A mechanistic understanding of electron-coupled proton transfer in photocatalytic CO₂ reduction is provided, offering an efficient pathway for advancing solar-driven hydrocarbon production technologies.